1. Field of the Invention
This invention relates to a superconducting cable consisting of a plurality of wires, each of which has several filaments of a superconducting material embedded in a matrix material, wherein the wires are stranded or plaited and soldered to wire bundles which are then stranded or plaited to rope which is in turn stranded or plaited to cable.
2. Description of the Prior Art
Superconducting cables are particularly used for the winding of coils which are intended for the excitation of very strong electromagnetic fields. According to the state of the art, the cable contains many ropes made from wire bundles. Two processes are used to cool the cable down to the temperature necessary for the superconduction: bath cooling in which the whole coil is immersed in a bath of a cooling medium; and forced cooling in which a cooling medium is pressed through the spaces between the wire bundles and the ropes (matrix cooling) and/or through cooling channels built into the cable (tubular conductor cooling). Cables intended to be matrix cooled are necessarily enclosed in a gas-tight case, while cables which are to be bath cooled preferably have no case.
On exciting magnetic coils, forces corresponding to the vectorial product of the exciting current and the magnetic induction act on the current conductors. These forces are directional and can cause a deformation of the conductors' cross section and the windings' cross section, as well as a change in the relative position of adjacent conductors. These deformations and changes of position can further cause a decrease in the contact pressure between neighboring conductors and/or a relative displacement of neighboring conductors. Both phenomena are particularly disadvantageous for superconducting cable.
During the relative displacement of adjacent conductors, heat can be generated from the resultant friction, which causes a small local rise in temperature and which is particularly disadvantageous at the operating temperature of superconducting cables.
The forces and the deformations caused thereby combine to produce a directional force on the inner wall of the casing, which can lead to an elastic deformation of the casing. For windings with tightly packed cable casings, the deformation forces of the cases are additive in the direction of the force, so that not only the associated Lorenz force, but in addition the mechanically transmitted deformation of the casing, acts on the individual cable.